1. Field of the Invention
The present invention relates to liquid crystal display devices. More particularly, the present invention relates to an apparatus and method for manufacturing a liquid crystal display device.
2. Discussion of the Related Art
Following the expansion of the information society, a need has arisen for displays that produce high quality images in thin, lightweight packages that consume little power. To meet such needs, research has produced a variety of flat panel display devices, including liquid crystal displays (LCD), plasma displays (PDP), electro luminescent displays (ELD), and vacuum fluorescent displays (VFD). Some of these display technologies have already been applied in information displays.
Of the various types of flat panel display devices, the LCD is probably the most widely used. In fact, in portable devices, such as notebook PC computers, LCD technology has already replaced cathode ray tubes (CRT) as the display of choice. Moreover, even in desktop PCs and in TV monitors, LCDs devices are becoming more common.
The basic LCD is comprised of opposing substrates and a liquid crystal material that is disposed between the substrates.
Liquid crystal represents a material phase that has properties between liquid and solid. Liquid crystal has the fluidity of a liquid, but the long-range crystal ordering of a solid. Liquid crystal has optical anisotropy due to its long-range crystal ordering and fluidity.
An LCD is manufactured using a number of processes, including array formation, color filter (CF) formation, liquid crystal filling (disposing), and module forming (described subsequently).
Array formation involves depositions, photolithography, and etching to form a thin film transistor (TFT) array on a first substrate (the TFT substrate). Color filter (CF) formation includes forming red, green, and blue color filters in a black matrix, and forming an ITO (Indium Tin Oxide) film that acts as a common electrode on a CF substrate.
The liquid crystal filling (disposing) process involves assembling the TFT substrate and the CF substrate together. Generally, the TFT and color filter substrates are mated to produce a thin gap between substrates. Then, liquid crystal is filled through a gap opening to form a liquid crystal panel.
In module forming, a driving circuit for processing input and output signals is connected to the liquid crystal panel. Additionally, frames are added to complete the liquid crystal module.
LCDs are typically assembled on a production line. In the prior art, cassettes, each having a plurality of TFT substrates or a plurality of color filter substrates, are input to a loader. Each TFT substrate includes a plurality of gate lines that extend in one direction, and a plurality of perpendicularly crossing data lines. Thin film transistors and pixel electrodes are arranged in a matrix at areas between the gate and data lines. The CF substrates each have a black matrix layer, a color filter, and a common electrode. Hence, the black matrix layer shields light leakage except for that desired from the pixel region.
Each TFT substrate or color filter substrate is individually removed from the cassette by the loader and transferred to the input of an alignment layer production line. That line, which includes a hand-programmed robot, forms an alignment layer on the individual substrates, reference alignment process step 1S of FIG. 1.
Step 1S includes cleaning individual substrates to enable formation of a uniform alignment layer coating. Then, an alignment material is coated on the substrate. Then, the alignment material is cured by drying off a solvent in the alignment material, and/or by inducing thermal polymerization of the alignment material. After curing, the alignment material is mechanically rubbed to induce a surface that anchors the liquid crystal in a uniformly align fashion. Finally, a cleaning process is carried out again, resulting in an alignment layer.
After the alignment layer 1S is completed, several processes are performed to produce a gap. Those processes can be carried out in serial or in parallel. The gap forming processes include a cleaning process (step 2S) in which a substrate (TFT or color filter substrate) is cleaned and a spacer scattering process (step 3S) in which spacers are scattered onto that substrate. The spacers are used to maintain the gap thickness constant and uniform.
Instead of forming a gap, a sealant coating process (step 4S) can be performed on the substrate (one type of substrate [TFT or CF] undergoes gap forming, the other undergoes sealant coating). After a cleaning step 2S, a sealing material is disposed on a peripheral part of the substrate. The sealing material is subsequently used to attach the TFT substrate to the CF substrate to form an assembled panel. It should be understood that the sealant coating process. (4S) is performed on one type of substrate (TFT or CF), while spacer scattering is performed on the other type. Thus, as shown in FIG. 1, the production line has two sub-portions. One sub-portion cleans (step 2S) and scatters spacers (step 3S). The other cleans (step 2S) and produces a seal (step 4S).
After the spacer scattering process 3S and the sealant coating process 4S, an assembling process (5S) that aligns, heats, and presses the TFT substrate and the color filter substrate together to produce an LCD panel is performed. In the assembly process, the TFT substrate and the color filter substrate are arranged in an opposing fashion and then joined to form an LCD panel.
After the assembly process (step 5S), a cutting process (step 6S) cuts the assembled empty LCD panel into a plurality of unit panels by scribing and breaking the assembled empty panel.
After the cutting process (step 6S) is complete, liquid crystal is filled into the unit panels through a liquid crystal filling hole in the sealing material and the filling hole is then sealed (step 7S).
Finally, after step 7S, the individual liquid crystal unit panels are ground (to removed shorting bars), and inspected, reference step 8S. The liquid crystal cell is then complete.
A typical prior art liquid crystal injection process per step 7S is schematically illustrated in FIG. 2. As shown, liquid crystal 1 is put into a vessel 3. The vessel 3 is inserted in a vacuum chamber 2. The vacuum chamber 2 is evacuated for a period of time to remove water adhering to an inner wall of the vessel 3, water in the liquid crystal 1, and micro bubbles in the liquid crystal 1.
Still referring to FIG. 2, the seal opening of several unit panels 4 are then dipped into the liquid crystal. Inflowing N2 gas produces atmospheric pressure in the chamber 2. The pressure difference between the vacuum in the unit panels 4 and the chamber 2 forces liquid crystal into the unit panels.
After the respective unit panels 4 have been charged with liquid crystal 1, the liquid crystal inlet is sealed. The unit liquid crystal panels are then cleaned. This completes step 7S.
While beneficial, liquid crystal injection using the foregoing procedures has problems. For example, the illustrated liquid crystal injection method requires a long time, such as over 10 hours to fill a ten-inch panel. The injection time is so long because the gap thickness between the substrates is very small and the area to be filled is relatively large. This problem is particularly acute when fabricating a large area LCD. Additionally, the foregoing process wastes liquid crystal due to the fact that excess liquid crystal material cannot be reused because the liquid crystal may be contaminated and/or degraded by impurities and chemical reactions. To overcome such problems a method of applying liquid crystal using a dropping method has been proposed.
The liquid crystal dropping method is briefly explained with reference to FIG. 3. It should be understood that the TFT and color filter substrates are beneficially large glass substrates that include a plurality of substrate panel areas (TFT arrays and color filter arrays) that will eventually form individual LCD displays. In the liquid crystal dropping method, liquid crystal is dropped onto substrate panel areas of a substrate. The dropped liquid crystal will be subsequently spread over the substrate panel areas when the first and second substrates are assembled together.
As shown in FIG. 3, liquid crystal 25 is dropped onto the substrate panel areas of a TFT substrate 20 (alternatively, the CF substrate) before assembling the TFT substrate 20 and the CF substrate 30 together.
Assuming liquid crystal is dropped onto the TFT substrate 20, a sealing material 35 is dispensed onto the periphery of the substrate panel areas of the color filter substrate 30. After the liquid crystal is dropped and the sealing material is dispensed, the TFT substrate 20 and the color filter substrate 30 are assembled together into a liquid crystal panel having a plurality of unit liquid crystal panel areas. Substrate assembly requires aligning, evacuating, and pressing. Assembly pressure forces the liquid crystal to spread out to form a uniform liquid crystal layer in each of the unit liquid crystal panel areas.
In the liquid crystal dropping method, liquid crystal can be quickly dropped (applied) onto the substrate panel areas. Therefore, the liquid crystal dropping method is highly time efficient, particularly for large area liquid crystal panels. Further, since pre-determined amounts of liquid crystal are dropped, liquid crystal consumption is minimized, reducing cost and waste.
Unfortunately, even the liquid crystal dropping method has problems. One set of problems, discussed below, is a result of having multiple substrate panel areas on each substrate.
As previously explained, the TFT substrate and the color filter substrate include a plurality of substrate panel areas that will eventually form a plurality of individual liquid crystal panels. For example, FIG. 4 shows four substrate panel areas on a first substrate 100, and four substrate panel areas on a second substrate 200. Those substrate panel areas will eventually be matched together. Still referring to FIG. 4, the first substrate 100 and/or the second substrates 200 may include a NG (no good/defective) substrate panel area.
After the first substrate 100 and the second substrate 200 are assembled into a composite liquid crystal panel, the unit liquid crystal panel areas having good TFT and good CF substrate panel areas can produce good unit liquid crystal panels. However, a unit liquid crystal panel area having an NG TFT and/or an NG CF substrate panel area is defective.
Moreover, as the number of the substrate panel areas on the substrates increase, more NG substrate panel areas are matched with good substrate panel areas (or with other NG substrate panel areas). After the unit liquid crystal panels are cut into individual liquid crystal panels, unnecessarily processing of NG individual liquid crystal panels, such grinding, cleaning, and testing is performed. This wastes worker's time and increases processing costs.
Therefore, a method of avoiding unnecessary processing of NG individual liquid crystal panels would be beneficial.